Virtual Chassis
What Is a Virtual Chassis System?
A collection of interconnected EX 4200 switches that are represented and managed as a single entity
?Consists of 1 to 10 EX 4200 switches
?Provides a scaling solution within a switching environment ?Allows up to 480 10/100/1000 Ethernet ports
Benefits of a Virtual Chassis System
?Managed as a single switch
?Simplifies management tasks such as software upgrades ?Spanning Tree Protocol is not required within Virtual Chassis systems
?Provides control plane redundancy
?Facilitates master and backup Routing Engine election and management
?Allows growth and expansion based on needs ?Start with a single EX 4200 switch and grow as needed (up to a maximum of 10 EX 4200 switches)
?EX 4200 platform switches
?1 to 10 EX 4200 switches can be interconnected
?Varying EX 4200 platforms supported in Virtual Chassis systems
?PFE
?Each EX 4200 switch has 2 or 3 PFEs
?24-port platforms have 2 PFEs
?48-port platforms have 3 PFEs
?The PFEs interconnect to form the backplane
?VCPs:
?Use proprietary VCB cables
?VCPs are located on the rear of EX 4200 switches
?Each EX 4200 switch comes with a .5 meter VCB cable ?Longer VCB cables are available
?No configuration required
?Ports can be enabled or disabled
?VCEPs:
?Use fiber optics to connect remote member switches ?Require 2x10 Gigabit Ethernet uplink module
?Must be enabled
Deployment Options
Some common deployment options include:?Single-rack application
?Generally spans less than 5 meters
?Top-of-rack application
?Can span up to 15 meters
?Remote wiring closet application
?Uses VCEPs to interconnect switches in remote wiring closets; can
span more than 500 meters
Single-rack application:
Top-of-rack application:
Remote wiring closet application:
Distribution
Closet -East Closet -West
10-Gigabit VCEP
10-Gigabit Uplink
VCP
Recommended process:
1.Install desired master switch
?Power up desired master switch—switch becomes master and
obtains member-id 0
?Assign mastership priority (255) 2.Add desired backup switch
?Connect to master using VCB cable
?Power up desired backup switch—switch is elected as backup and
assigned member-id 1
?Assign mastership priority (254)
1
2
3
4 Linecard
Backup (Backup RE) Master (Active RE) Linecard
Linecard
ON
ON
Recommended process (contd.):
3.Add line card switch
?Connect to switch above with VCB cable ?Power up third switch—switch becomes
line card and is assigned
member-id 2
?Assign desired mastership priority
4.Repeat Step 3 to add subsequent
line card switches
?Last line card switch completes loop by
connecting with master
1
2
3
4 Linecard
Backup (Backup RE) Master (Active RE) Linecard
Linecard
ON
ON
ON
ON
ON
Connectivity
?Single management interface
?Individual management Ethernet ports on member switches are tied to a special management VLAN associated with a
Layer 3 virtual management interface (vme)
?Single management IP address
?The Virtual Chassis system is managed as a single network element; therefore, it has only one management IP address ?Single virtual console
?Connection to a console on any member switch in a Virtual Chassis system is redirected to the VC master by virtual
console software running on all member switches
Software
?Software upgrades need be performed only on the master switch
?Software image compatibility check:
?Member switches must be running the same software
version as the master to be part of a Virtual Chassis system ?If a version mismatch exists, a syslog message is generated ?The master switch performs software compatibility checks on the JUNOS software version on each member switch ?Switches with different hardware versions or model numbers can
be members of the same Virtual Chassis system
?A CLI command is available to upgrade incompatible
switches by downloading the correct image from the master over the Virtual Chassis cable
Roles and Responsibilities
?Master switch:
?Manages all switches participating in the Virtual Chassis
system
?Runs JUNOS software in a master role
?Runs chassis management processes and control protocols ?Backup switch:
?Maintains a state of readiness should the master fail
?Receives synchronized protocol state and forwarding table
information from master switch
?Runs JUNOS software in a backup role
?Line card:
?The remaining member switches in the Virtual Chassis system are candidate switches operating as if they are line cards
Mastership Election
?Mastership determination:
1.Member with the highest user-configured priority
?Priority range is 1–255, factory-default value is 128
2.Member previously functioning as master prior to reboot
3.Member with the longest standing uptime
?Difference must be greater than 1 minute
4.Member with the lowest MAC address
?Used as tie breaker if all is equal through the first 3
determination points
?Configuring mastership priority:
[edit virtual-chassis]
user@switch# show
member 0 {
mastership-priority 255;
}
member 1 {
Mastership Election Considerations
Once the master is elected:
?The member that is second in the master election process becomes the backup switch
?If a master or backup fails, one of the line card switches is elected as the new backup switch
?Preemption occurs when a switch with a higher mastership priority joins the Virtual Chassis system
Member ID Assignment
Member ID assignment and considerations:?Master switch typically assumes member ID 0
?Master switch assigns unique member IDs (1–9) to each
member switch
?Member IDs are assigned in ascending order based on the sequence in which member switches were added to the
Virtual Chassis system
?Member ID is preserved across reboot within a Virtual
Chassis system
?Member ID serves as slot number for interface naming
?Member ID can be manually configured through the CLI
?VCCP is used to exchange LSA-based discovery messages
?Discovery messages are exchanged between all PFEs and
build member switch topology and PFE topology maps
?Each switch runs shortest-path algorithm for each PFE ?Creates PFE map tables that outline shortest paths between all PFEs
?Source ID egress filter tables prevent broadcast and multicast packets from looping
?Filter tables are built for each PFE
b c a e f d h i
g Physical Virtual Chassis Cabling Virtual Chassis Backplane Cables a i
b h d f e
c g Logical Virtual Chassis Ring Topology Virtual Chassis Backplane
Note: a, b, c, … i are PFEs
Example of topology discovery with the SPF algorithm:
Example of topology discovery with the SPF algorithm (contd.):
a
i b
h
d
f
e
c
g
Logical Virtual Chassis Ring Topology
Virtual Chassis Backplane Note: a, b, c, … i are PFEs
a
b
i
c
h
d
g
e
f PFE a’s Rooted Reachability SPF Tree
g
f
h
e
i
d
a
c
b PFE g’s Rooted Reachability SPF Tree